The invention relates to a weldable FBG strain sensor arrangement that is versatile in use due to its easy-to-vary and cost-effective construction.
Strains of material surfaces can e.g. be measured with strain sensors, which are mounted on these surfaces. When the surface is stretched or compressed, the strain sensors are impacted thereby, so that a measurement signal is generated.
In many cases, so-called strain gauges are used as strain sensors and secured by an adhesive on the surface to be measured. These strain gauges are made of epoxy-impregnated paper or a glass fiber fabric, on which a thin metal foil is attached. Strain gauges of this type can be used for a wide range of applications, because they can be attached at almost any location of a workpiece. Disadvantageous, however, is the substantial complexity of their attachment. There are situations in which such so-called metal foil strain gauges cannot be used. Upon their attachment, certain parameters such as ambient and workpiece temperatures and air humidity must be observed. Also, after the strain gauge has been attached, the measuring point must be protected against mechanical damage and ingress of moisture. This is achieved by protective covers. Against ingress of moisture, an adhesive film is used with an embedded water vapor barrier made of aluminum. In the event of great temperature fluctuations, this moisture protection may detach, however. In the case of dynamic measurements, shear forces occur at the measuring point and may also cause the detachment of this moisture protection. When a protection against mechanical contact is required in addition, a housing made of a mechanically resistant material is attached over the measuring point.
In order to avoid the afore-described cumbersome assembly steps, already encapsulated weldable strain sensors are used, such as e.g. shown in the documents DE 2658324 C2, JP 4519703 B2 and DE 10335337 A.
Document DE 10335337 A1 describes a so-called multipurpose strain sensor. This multipurpose strain sensor is mechanically robust and well protected against moisture, but has a complicated structure, as can be seen in FIG. 1 of the document DE 10335337 A1.
The object of the present invention is the provision of a robust strain sensor construction which, compared to the prior art, is significantly simpler in structure.